With the rapid development of network construction and customer application requirements of the mobile communication, the coverage and quality requirements of indoor signals are increasingly growing stronger. The active indoor Distributed Antenna System (DAS) has gradually become a preferable scheme for achieving high quality indoor in-depth coverage. There are coverage schemes of SISO (Single Input Single Output) and MIMO (Multi-input Multi-output) in the deployment of 4G LTE (as a general term for TD-LTE, FDD-LTE and other LTE network types) networks. The SISO coverage may be performed firstly in some places, and then the MIMO coverage may be performed. However, the existing DAS relay unit only supports one of SISO mode and MIMO mode, and is not configurable. Different DAS relay units are applied according to different schemes during the 4G (the fourth generation of mobile communication technology) network construction, and in this regard when SISO needs to be upgraded to MIMO, devices have to be replaced, which greatly increases the cost of the network construction.